There are many devices used in purification of molecules where an adsorptive media is packed into the bottom of a syringe-like object, or in the wells of a multiwell plate. Typically, the target solute is eluted in a buffer that is unfavorable to further analysis, and the solute must be further processed to remove or exchange the eluting buffer with another buffer favorable for further analysis or other use.
An example of such is an elution from an ion exchange column, wherein the solute of interest is eluted from the column in a high salt buffer. However, many subsequent analyses of the solute of interest, including, e.g., electrophoresis or enzymatic digests of plasmid DNA, cannot be performed satisfactorily in this high salt environment. Thus, at present, such a sample is often desalted with dialysis or with a separate gel permeation or size exclusion chromatography ("SEC") device, or for plasmid purification, the DNA is precipitated from the salt solution with a variety of precipitants, including ethanol, isopropanol, PEG4000, and the like. (See, e.g., U.S. Pat. No. 5,057,426 to Henco et al., which is incorporated herein by reference.)
In addition, prior to the present invention, adsorptive chromatography devices which used multiwell plates required a two step/two plate method in order to achieve purification, by e.g., ion exchange, and subsequent separation of the desired product from the high salt content of the elution buffer. This required using two separate chromatography steps and two multiwell plates, thereby undesirably increasing both the time and cost of such purification methods.